[5591945][5589019@13][ONNX] Fix 'nodes not sorted' failure (#507)

## What does this PR do?

**Type of change:** Bug fix

**Overview:** Ensure nodes are topologically sorted in ONNX graph.

## Usage

```python
python -m modelopt.onnx.quantization --onnx_path=$MODEL_NAME.onnx
```

## Testing
See bug 5591945 (model 4) and 5589019@13.

## Before your PR is "*Ready for review*"
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- **Make sure you read and follow [Contributor
guidelines](https://github.com/NVIDIA/TensorRT-Model-Optimizer/blob/main/CONTRIBUTING.md)**
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- **Is this change backward compatible?**: Yes
- **Did you write any new necessary tests?**: No
- **Did you add or update any necessary documentation?**: No
- **Did you update
[Changelog](https://github.com/NVIDIA/TensorRT-Model-Optimizer/blob/main/CHANGELOG.rst)?**:
No

---------

Signed-off-by: gcunhase <4861122+gcunhase@users.noreply.github.com>

Author: gcunhase

modelopt/onnx/trt_utils.py

@@ -321,6 +321,11 @@ def load_onnx_model(
             # Infer types and shapes in the graph for ORT compatibility
             onnx_model = infer_types_shapes_tensorrt(onnx_model, trt_plugins or [], all_tensor_info)
 
+    # Ensure nodes are topologically sorted
+    graph = gs.import_onnx(onnx_model)
+    graph.toposort()
+    onnx_model = gs.export_onnx(graph)
+
     # Enforce IR version = 10
     ir_version_onnx_path = None
     if onnx_model.ir_version > MAX_IR_VERSION: